The present invention relates generally to a radio antenna and, more specifically, to an internal multi-band antenna for use in a hand-held telecommunication device, such as a mobile phone.
The development of small antennas for mobile phones has recently received much attention due to size reduction of the handsets, requirements to keep the amount of radio-frequency (RF) power absorbed by a user below a certain level regardless of the handset size, and introduction of multi-mode phones. It would be advantageous, desirable and even necessary to provide internal multi-band antennas to be disposed inside a handset body, and these antennas should be capable of operating in multiple systems such as E-GMS900 (880 MHz-960 MHz), GSM1800 (1710 MHz-1880 MHz), PCS1900 (1859 MHz-1990 MHz) and UMTS (1900 MHz-2170 MHz). Shorted patch antennas, or planar inverted-F antennas (PIFAs), have been used to provide two or more resonance frequencies. For example, Liu et al. (Dual-frequency planar inverted-F antenna, IEEE Transaction on Antennas and Propagation, Vol.45, No.10, October 1997, pp. 1451-1458) discloses a dual-band PIFA; Pankinaho (U.S. Pat. No. 6,140,966) discloses a double-resonance antenna structure for several frequency ranges, which can be used as an internal antenna for a mobile phone; Isohatala et al. (EP 0997 970 A1) discloses a planar antenna having a relatively low specific absorption rate (SAR) value; and Song et al. (Triple-band planar inverted-F antenna, IEEE Antennas and Propagation International Symposium Digest, Vol.2, Orlando, Fla., Jul. 11-16, 1999, pp.908-911) discloses a triple-band PIFA. As mobile phones capable of operating at the UMTS frequencies will become a reality in near future, it is advantageous and desirable to provide an antenna structure capable of operating in the UMTS frequencies as well as the GSM frequencies.
According to first aspect of the present invention, a multi-band radio antenna structure for use in a hand-held telecommunication device comprises:
a ground plane;
a sub-antenna structure comprising:
a first radiating element formed of a first electrically conducting area having a first resonance frequency, wherein the first electrically conducting area has a first end connected to the ground plane for grounding the first radiating element, and wherein the first radiating element has a first feed-point for feeding located adjacent to the first end; and
a second radiating element formed of a second electrically conducting area disposed adjacent to the first electrically conducting area, wherein the second electrically conducting area has a second end electrically connected to the first end of the first electrically conducting area for grounding the second radiating element and for sharing the first feed-point for feeding;
a third radiating element formed of a third electrically conducting area adjacent to the sub-antenna structure, wherein the third electrically conducting area has a third end connected to the ground plane for grounding the third radiating element, and wherein the third radiating element has a second feed-point for feeding located adjacent to the third end;
a first switching device, operable either in an open position or in a closed position, connecting between the first feed-point and the ground plane; and
a second switching device, operable either in an open position or in a closed position, connecting between the second feed-point and the ground plane, wherein
when the second switching device is operated in the closed position, thereby grounding the second feed-point and the first switching device is operated in the open position for enabling the first feed-point feeding, the second radiating element has a second resonance frequency substantially lower than the first resonance frequency and the third radiating element has a third resonance frequency generally higher than the first resonance frequency, and
when the first switching device is operated in the closed position, thereby grounding the first feed-point and second switching device is operated in the open position for enabling the second feed-point feeding, the third radiating element has a fourth resonance frequency generally higher than the third resonance frequency.
According to the present invention, when the first switching device is operated in the closed position and the second switching device is operated in the open position, the first radiating element has a fifth resonance frequency substantially equal to the third resonance frequency.
According to the present invention, the first resonance frequency is substantially in a frequency range of 1710 MHz to 1880 MHz, the second resonance frequency is substantially in a frequency range of 880 MHz to 960 MHz, the third resonance frequency is substantially in a frequency range of 1850 MHz to 1990 MHz, and the fourth resonance frequency is substantially in a frequency range of 1920 MHz to 2170 MHz.
According to present invention, the third electrically conducting area is adjacent to the first electrically conducting area or adjacent to the second electrically conducting area.
According to the present invention, the first and the second radiating elements are planar radiating elements located substantially on a common plane.
According to the present invention, the first, second and third radiating elements are planar radiating elements located substantially on a common plane.
According to the present invention, the first, second and third radiating elements are planar radiating elements but some or all of the radiating elements can be folded such that each of the folded radiating elements is located in two or more intersecting planes.
According to the second aspect of the present invention, a method of achieving at least four resonance frequencies in a multi-band antenna structure including:
a ground plane;
a sub-antenna structure comprising:
a first radiating element formed of a first electrically conducting area having a first resonance frequency, wherein the first electrically conducting area has a first end connected to the ground plane for grounding the first radiating element, and wherein the first radiating element has a first feed-point for feeding located adjacent to the first end; and
a second radiating element formed of a second electrically conducting area disposed adjacent to the first electrically conducting area, wherein the second electrically conducting area has a second end electrically connected to the first end of the first electrically conducting area for grounding the second radiating element and for sharing the first feed-point for feeding;
a third radiating element formed of a third electrically conducting area adjacent to the sub-antenna structure, wherein the third electrically conducting area has a third end connected to the ground plane for grounding the third radiating element, and wherein the third radiating element has a second feed-point for feeding located adjacent to the third end, said method comprising the steps of:
providing a first switching device, operable either in an open position or in a closed position, connecting between the first feed-point and the ground plane;
providing a second switching device, operable either in an open position or in a closed position, connecting between the second feed-point and the ground plane; and
setting the second switching device in the closed position, thereby grounding the second feed-point and the first switching device in the open position for enabling the first feed-point feeding, so as to cause the second radiating element to produce a second resonance frequency substantially lower than the first resonance frequency and the third radiating element to produce a third resonance frequency generally higher than the first resonance frequency, or
setting the first switching device in the closed position, thereby grounding the first feed-point and second switching device in the open position for enabling the second feed-point feeding so as to cause the third radiating element to produce a fourth resonance frequency generally higher than the third resonance frequency.
According to the present invention, when the first switching device is set in the closed position and the second switching device is set in the open position, the first radiating element to produce a fifth resonance frequency substantially equal to the third resonance frequency.
The present invention will become apparent upon reading the description taking in conjunction with FIGS. 1 to 3b. 